#include <stdio.h>
double Sum(int a,int b) 
{
	int i = a;
	double sum = 0;
	for (i = a; i < b+1; i++) 
	{
		if ((i - a + 1) % 2 == 0)
			sum -= 1 / (double)i;
		else
			sum += 1 / (double)i;
	}
	return sum;
}
int main() 
{
	int a, b;
	scanf_s("%d %d",&a,&b);
	printf("%lf",Sum(a,b));
	return 0;
}